weighted random selection

[Doublearon]

Currently I have a MySQL table that has a list of advertising traffic affiliates for a site I'm doing the scripting for. The table has the domain, incoming, and outgoing hits and I currently use mt_rand (seeded with mt_srand) to select a table row (a trade affiliate) to send traffic to. However, I'm thinking if I could weight the random selction somehow, I could weight the outgoing traffic towards those affiliates that send more traffic.

Does anyone know of a way to do "weighted random" selection?

[diego25]

Well, I don't know if PHP or MySQL have a built-in way of doing it, but you could do it manually.

If, for example, you have 2 traffic sites, A and B. And you want the weight of A to be 2 and the weight of B to be 1. Therefore, the total weight is 3, and A would have 2/3 and B 1/3.

You also know that PHP's rand() function returns a value from 0 to RAND_MAX. Therefore, by letting 2/3 of the 0 to RAND_MAX range be A, and 1/3 be for B, you can have a weighted random number.

So, for example, if RAND_MAX is 11. Then there are 12 values that rand() can return, 0,1,2,3,4,.., 10, and 11. So, if the first 2/3 belong to A, in other words 0,1,2,3,4,5,6,7. And the last 1/2 goes to B: 8,9,10,11. Then the chances of rand() returning a value for A is double the chances for B, just because the range is double.

Hope that made sense 🙂

Diego